We found this circuit in a 1994 National Semiconductor technical documentation. The circuit can be adapted to operate with more modern equivalent operational amplifiers.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...